1. Field of the Invention
This invention relates to a deferred actuated batteries, and more particularly to an improved deferred actuated battery assembly including an electrochemical cell having a hybrid cathode.
2. Description of the Prior Art
Battery requirements for marine data systems vary from a few milliwatts for CMOS instrumentation to several tens of kilowatts for the operation of a mini autonomous underwater vehicle (AUV). Nonaqueous lithium cells and zinc-based primary cells, as well as nickel-cadmium and lead-acid batteries, are currently used. Safety and the corrosive nature of the electrolyte and/or some cathode materials used in such power sources dictate that cells and batteries be well sealed to prevent leakage and/or rupture during storage and use. Lithium batteries use hermetic seals with safety vents and a fuse. Alkaline cells are rendered leakproof by suitable double crimp joints. Lead-acid cells use a gelled electrolyte to prevent spillage of the electrolyte. Such techniques have minimized the hazards of handling and use, however at the expense of the costs. Sealed cells require a "pressure hull" enclosure for deep sea application and thus use of a pressure hull significantly reduces energy density and concomitantly increases usage cost. Other types of power cells used in undersea applications are water activated magnesium batteries with a bipolar configuration as open cells. A magnesium anode and a metal halide-based cathode allows the use of sea water as the electrolyte and do not require a pressure hull housing for deep sea applications.
Deferred actuated batteries, such as silver chloride-magnesium batteries using sea water as an electrolyte have been used for years, and are expensive being based upon the use of a precious metal, i.e. silver. Subsequent developments centered on non-silver containing sea water actuated batteries, e.g. U.S. Pat. No. 3,462,309 to Wilson based upon a magnesium anode-inert metal cathode type of a serial flow type configuration provided limited usages as well as extensive electrical circuitry including tunnel diode inverters to provide useful voltage levels. In U.S. Pat. No. 4,185,143 to Brit et al., there is disclosed a water actuated battery based upon metal/organo halogen couples having anode and cathode members of planar form with a porous insulating member sandwiched therebetween where the cell is provided with electrolyte access passageways extending around the periphery of the cathode member whereby electrolyte flowing in the passageway access the whole peripheral edge region of the cathode reactant material.
In U.S. Pat. No. 4,910,104, assigned to the same assignee as the present invention, there is disclosed a deferred actuated battery assembly comprised of a plurality of bipolar electrodes disposed between an inert cathode current collector acting as a hydrogen electrode and an anode plate formed of a material selected from the group consisting of aluminum, magnesium, aluminum alloys, magnesium alloys and mixtures thereof and configured for electrolyte flow therebetween. While such battery assembly has provided in a battery system improved capacity, longer shelf life, etc., there is always the desire to improve any such battery system, particularly with respect to current density.
In U.S. Pat. No. 4,910,102, assigned to the same assignee as the present invention, there is disclosed a deferred actuated battery assembly configured for hydrogen peroxide-containing electrolyte flow. Thus, the battery systems for marine duty are generally based upon dissolved oxygen in the seawater (DOS) as the cathode active material, e.g. magnesium/copper cells developed for underwater electrochemical power source. The concentration of DOS is about 6 ml. of dissolved oxygen per liter at the ocean surface and decreasing to low values (less than 1.5 ml. of dissolved oxygen per liter) depending on the depth and geographical location. Magnesium/copper cells fail to operate at such a low level concentration of DOS and to overcome such limitation, lead-acid battery systems are provided as back-up. Any back-up battery system has limited service-life, requires recharging, expensive pressure-hull housing as well as presents an increasing risk of explosion hazard due to hydrogen accumulation.